Seeds such as brassica seeds, and especially rapeseed, are potential sources of high-quality protein. After oil extraction, rapeseed meal contains about 38% protein compared to approximately 44% in soybean meal, the latter being widely used for feed and food purposes. Proteins contained in rapeseed are rich in lysine and contain adequate quantities of methionine, both of which are limiting amino acids in most cereal and oilseed proteins.
U.S. Pat. Nos. 4,889,921 and 6,905,713 (each to Diosady) disclose a process for isolating proteins from defatted rapeseed meal. The process comprises extracting the meal with an alkaline solvent, removing the meal residue, adjusting the pH of the extraction solution to obtain a precipitated protein product, and separating the unprecipitated protein from any undesirable components in the solution by membrane filtration.